Dictionary.net

Regulatory and structural genes present in certain bacteria, algae and fungi that control the conversion of atmospheric nitrogen into biologically usable compounds; include nif structural genes (e.g., nifD, nifH) for nitrogenase and nitrate reductase as well as regulator genes nifA, nifB, ntrA, ntrB, ntrC. Some are responsible for regulating transcription of genes involved in the assimilation of poor nitrogen sources in enteric bacteria.